Tensile Plastic Deformation Research Articles

Fatigue life of the welding seam of a tracked vehicle body structure evaluated using the structural stress method

The supporting roller is an important component in the driving systems of tracked vehicles. Through the bracket structure, the supporting roller is bolted to the vehicle body welded with a reinforced metal plate, providing vertical support and lateral guidance of the track. The strengthening weld structure between the bottom plate and the vehicle body is the root of the cantilever beam, where stress is concentrated and fatigue damage is easily accumulated. The fatigue life of the whole vehicle is affected by the fatigue damage in this part. This paper proposes a structural stress method to evaluate the fatigue life of the welding seam of a tracked vehicle body. Further, the proposed method is evaluated under typical road-load spectra. Initially, the base-metal and weld structures were subjected to monotonic tensile and cyclic plastic deformation tests. The tensile strength of the weld sample was approximately half of that of the base metal. Next, the welded structure of the supporting roller bracket was simulated using a finite element model. The calculated stresses were consistent with the fatigue crack locations in the welded structure. The structural stress was not dependent on the grid density. Subsequently, multibody dynamic simulations of the whole tracked vehicle were performed on four standard road surfaces constructed using the harmony superposition method. The road-load spectra at the axle head of the supporting roller were calculated under four pavement conditions, and the fatigue life of the weld structure of the supporting roller bracket was determined. The calculated fatigue life was considerably lower than the designed fatigue life. Finally, the initial weld structure was redesigned by increasing the size of the strengthening metal plate and the weld length. The fatigue life of the redesigned structure was considerably longer than that of the original structure, indicating that the proposed method can effectively analyze the fatigue life of the welding seam and that it can be used to optimize the design scheme.

Investigation of tensile creep behavior of Mg–Gd–Y–Zr alloy based on creep constitutive model

The tensile creep behavior of as-extruded and T6 treated Mg–8Gd–3Y–0.3Zr (GW83) alloy was estimated under temperature at 170–200 °C and stress at 40–70 MPa. The results showed that the primary creep strain and steady state creep rate increased, while the duration of steady state creep decreased with increasing temperature and stress. The primary creep constitutive model of GW83 alloy kept an Andrade power law ε = βt k with k value of 0.24–0.6 for as-extruded alloy and 0.13–0.49 for T6 alloy, respectively. The steady state creep plastic deformation of as-extruded and T6 state alloys can be expressed by Arrhenius constitutive equations with stress exponents 5.6–5.9 and 8.9–9.8, creep activity energy 124.9–135.6 kJ/mol and 152.2–195.8 kJ/mol, respectively. The tensile creep resistance of GW83 alloy improved significantly by T6 heat treatment, the effect of temperature on steady state creep rate was relatively moderate, and the tensile creep plastic deformation of GW83 alloy mainly was controlled by applied stress. The steady state creep deformation mechanism of as-extruded GW83 alloy was regulated by Mg self-diffusion conducted by dislocation climb before heat treatment, and then transformed to dislocation cross-slip after T6 treated. The recrystallization and texture evolution of (10) , (10) played a non-ignorable effect on the tensile creep deformation. The creep rupture life can be predicted by steady state creep rate that will be controlled by temperature under low and intermediate stress and by stress under larger applied stress, respectively. The creep fracture surfaces with coarse dimples and tear ridges presented as ductile transgranular fracture features with the secondary cracks occurred.

Dynamic Tension Deformation of Rare-Earth Containing Mg-1.9Mn-0.3Ce Alloy Sheet along the Rolling Direction at Various Temperatures

The tensile properties of rare-earth containing Mg-1.9Mn-0.3Ce alloy sheet along the rolling direction were experimentally investigated within the strain rate and temperature ranges of 0.001–1300 s−1 and 213–488 K. The obtained stress-strain responses of the alloy sheet indicate that both yield strength and strain-hardening rate increase when the strain rate increases, whereas they decrease with increase of temperature. Microscopic examination results show that basal slip, prismatic slip, and {101¯2} tension twinning take place in the tensile plastic deformation, while the occurrence of twinning is not obviously affected by the rate and temperature. Tensile samples tend to fracture in a ductile mode with increasing strain rate and temperature.

In situ synchrotron X-ray diffraction analysis of deformation behavior of a Nb/NiTi composite for biomedical applications

The deformation behavior involved in Nb/NiTi composite for biomedical applications within a large macroscopic strain range was investigated by tensile loading–unloading test and in situ synchrotron X-ray diffraction (SXRD). Experimental results show that during loading, the Nb/NiTi composite experiences the elastic elongation of B2-NiTi austenitic, B19′-NiTi martensitic and β-Nb phases, B2 → B19′ stress-induced martensitic (SIM) transformation and tensile plastic deformation of β-Nb phase. During unloading, the deformation behavior involved in Nb/NiTi composite includes the elastic recovery of B2-NiTi austenitic, B19′-NiTi martensitic and β-Nb phases, reverse phase transformation B19′ → B2 and compressive deformation of β-Nb phase. The martensitic transformation in this composite is almost reversible and occurs in a localized manner. These results might contribute to a comprehensive understanding of the deformation mechanism involved in Nb/NiTi composite and shed some light on design and development of novel composites with a combination of good biocompatibility and excellent superelasticity for biomedical applications.

Numerical and experimental investigation of tool geometry effect on residual stresses in orthogonal machining of Inconel 718

Residual stress has become more important than ever with the increasing performance requirement of components especially for those applied in safety-critical areas. As the machining process is fundamentally correlated with the acquired component properties, it is essential to fully understand the formation mechanism of residual stresses in the cutting process and its influence on the performance of the component. This paper presents results based on numerical and experimental analysis on the effect of tool geometry on thermal-mechanical load and residual stresses in orthogonal machining Inconel718 alloy. The Coupled Eulerian-Lagrangian (CEL) method is used to simulate the effect of tool geometry on temperatures, forces, equivalent plastic strains, and residual stresses. The local normal/tangential stress is introduced to determine the degree of the tensile plastic deformation induced by the tool. It is observed that a negative rake angle and a sharp edge radius tool tend to generate more compressive stress on the machined surface than the ones generated with positive rake angle tools and/or lager edge radius. Besides, an increase in flank wear produces less magnitude of compressive stress in subsurface due to a decreased local normal stress caused by increased flank contact length.

Promotion of Ionic Conductivity of PEO-Based Solid Electrolyte Using Ultrasonic Vibration.

All solid-state lithium-ion batteries based on polymer electrolytes have higher safety and energy density, but the low conductivity of lithium ion restricts its application. This study proposes a new method to promote the ionic conductivity of polyethylene oxide (PEO)-based solid electrolytes. In this method, the PEO-based solid electrolyte was first prepared by casting, and then power ultrasound was exerted on the electrolyte by a sandwich structure to modify the electrolyte structure. Through analysis of the performance and microstructure of the electrolyte, it was found that the ultrasonic treatment increased the ionic conductivity by 78%, improved tensile strength and plastic deformation ability, but did not affect the thermal stability and the chemical composition. The ultrasonic vibration, exerting high energy to the solid electrolyte through high-frequency vibration, broke PEO grains and melted them with the frictional heat at boundary. Due to the slight melting and fast solidifying produced by the pulsed ultrasonic treatment, the crystallization was suppressed. The crystallinity was thus reduced by 6.2%, which increased the migration channels of lithium ions and reduced the tortuosity effect. Furthermore, the ultrasonic vibration compressed the electrolyte to produce plastic flow of the material, which made the electrolyte structure more compact. The density of ethylene oxide (EO) units thus increased in the amorphous phase, providing multiple electron-donor coordination sites for the Li+. The hopping distance of the ion between donors decreased, which also facilitated the migration. In addition, the mechanical performance of the electrolyte membrane improved. This study provides a reference for the improvement of polymer based all-solid-state batteries.

Analysis of Strain Aging of Steel Sheets by In Situ Electrical Resistance Measurement

ABSTRACTObservation of the dynamic interaction between dislocations and carbon atoms is important in steel design. Some steel materials are bake-hardened in several manufacturing processes. Solute carbons are known to segregate on dislocations; this hardens the steel even after low-temperature treatments. The purpose of this study was to develop a method of monitoring a series of microstructural changes in strain aging by in-situ measurement of the electrical resistance in low-carbon steel. In tensile deformation, elastic, Lüders, and uniform plastic deformations could be distinguished by monitoring the changes in electrical resistance. Electrical resistance rapidly increased in the plastic deformation region in the strain-aged specimen. Although the deformation stress hardly changed, the amount of lattice defects monotonously increased. These analyses provide useful information in steel design related to thermomechanical treatments of bake-hardenable steel.

Deformation Behavior and Dynamic Recrystallization of Ti–22Al–25Nb Alloy at 750–990 °C

Ti–22Al–25Nb is a representative of Ti2AlNb alloys with excellent comprehensive properties, which has great application prospects in the aerospace field. Herein, high‐temperature tensile plastic deformation behavior and dynamic recrystallization process of Ti–22Al–25Nb alloy are researched during 750–990 °C. From 750 to 870 °C, plasticity is gradually improved with temperature increasing, and the fracture mode is crack aggregation. From 900 to 930 °C, the content of B2 phase increases and plasticity is significantly improved because crack along the grain is suppressed by combined precipitation of three phases B2 + O + α2 at grain boundaries with large areas. From 960 to 990 °C, the alloy is mainly composed of B2 phase and has best plastic deformation performance. Fully dynamic recrystallization of B2 phase happens at 990 °C. Texture strength is strengthened by intense plastic deformation, but it is weakened by dynamic recrystallization subsequently.

Economical Si-Bearing, Nearly Ni-Free 19Cr TRIP-Aided Duplex Stainless Steels with Better High-Temperature Oxidation Resistance

A novel series of Si-bearing, nearly Ni-free economical TRIP-aided duplex stainless steels (DSSs) 19Cr-5.5Mn-0.3Ni-0.2N-xSi (x = 0.5-2.5) have been prepared to investigate effect of silicon on microstructure, tensile mechanical property and high-temperature oxidation behavior. The results have shown that the designed economical alloys have a balanced ferrite/austenite dual-phase structure after suitable solution treatment. Volume of ferrite phase increases with an increase in silicon content. Ferrite deforms by dislocation slip during tensile plastic deformation process at room temperature. However, transformation-induced plasticity effect dominates deformation mode of metastable austenite phase. The designed DSS with 1.5 wt.% Si content exhibits good combination of tensile mechanical properties, exceeding 50% in elongation and 800 MPa in ultimate tensile strength, with a sequential γ → e-martensite → α′-martensite transformation in deformed austenite phase. High-temperature oxidation resistance of DSSs could be enhanced with an increase in silicon content at 1100 °C in air due to the formation of compact and continuous Cr- and Si-rich oxide film in the inner oxide film layer.

Plastic deformation mechanism of MWCNTs/AZ91D nanocomposites with high ductility at room temperature

1.0 wt% MWCNTs/AZ91D magnesium matrix nanocomposites were prepared by metal mold gravity casting process assisted by high-intensity ultrasonic dispersion, and the ductility was further improved by T4 solid solution treatment. The tensile test results at room temperature revealed that the tensile strength and elongation of 1.0 wt% MWCNTs/AZ91D nanocomposites after T4 solid solution treatment reached up to 281.7 MPa and 15.4%, respectively. The ductility of magnesium matrix nanocomposites was significantly improved by the addition of Multiwalled carbon nanotubes (MWCNTs) and T4 solid solution treatment. SEM and TEM were used to observe the microstructure of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites after the tensile plastic deformation at room temperature. A considerable number of slip bands and twins were found in the microstructure of the nanocomposites. High strain zones were formed around MWCNTs during the tensile process at room temperature. A large number of dislocations and stacking faults were generated in the high strain zones, which could be used as the origin of slip bands and twins, so MWCNTs can promote slip and twining. MWCNTs can further activate non-basal slip and cross slip, and improve the ductility of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites.

A model for the influence of plastic deformation on Magnetic Barkhausen Noise in carbon steel

In this work, a model for the influence of tensile plastic deformation on Barkhausen Noise is proposed. This model is based on a previous model that allows to explain the influence of magnetizing parameters, applied field frequency and electric conductivity on Barkhausen Noise. In order to analyze the effects of plastic deformation on Barkhausen Noise, the model was modified to include the presence of dislocations tangles, the change of the mean coercivity and the change of local coercive field standard deviation as a function of the tensile plastic deformation. The simulations of the model are compared with Barkhausen signal, obtained from three different steel subjected to six levels of plastic deformation. The experimental results show that the amplitude of Barkhausen signal decreases, the main peak field increases and the signal envelope width increases with the increase of tensile plastic deformation. The simulated Barkhausen envelope shows the same behavior as the experimental envelope considering that the number of dislocation tangles increase, the mean value of the local coercive field increases and the standard deviation of the local coercive field increases with the increase of plastic deformation.

Tensile Behavior and Deformation Mechanism of Fe-Mn-Al-C Low Density Steel with High Strength and High Plasticity

Tensile behavior and plastic deformation mechanisms of Fe-22.8Mn-8.48Al-0.86C low-density steel were studied in this thesis. After solution treatment 1100 °C for 1 h; the steels obtained an excellent combination in mechanical properties; with tensile strength of 757.4 MPa and total elongation of 68%; which were attributed to the existence of annealing twins in austenite. The present steel presented a multiple stage strain hardening behavior which was associated with the changes of such dislocation substructures. With the increase of strain, the gradual transition from tangled dislocations to dense dislocation walls and microbands was found in (the transmission electron microscopy) TEM microstructures. Due to the influence of the evolution of the microstructure during the deformation process, the work hardening behavior of the experimental steel shows three distinct stages.

Effect of tensile deformation on variant selection in {225}γ plate martensite and {557}γ lath martensite

The effect of tensile deformation on variant selection has been studied in {225}γ plate martensite and {557}γ lath martensite formed in high- and low-carbon steels, respectively. Different thermomechanical treatments are performed to analyse the effect of applied tensile stress, in the elastic and plastic range and the effect of prior plastic tensile deformation on variant selection. The variant selection is studied by computing the work of the deformation associated with the transformation in the applied stress field. Our analysis indicates that the deformation that needs to be considered to model the selection is based on lattice strains combinations. For {225}γ plate martensite, the average deformation resulting from the combination of the lattice strains of twin-related variants is the relevant deformation gradient for the work computation. On the contrary, in lath martensite, the combination of the lattice strains of low-misoriented variants appears to better model the selection phenomenon.

Al/Niobium Diboride Nanocomposite’s Effect on the Portevin-Le Chatelier Phenomenon in Al-Mg Alloys

In Al-Mg alloys, the Portevin-Le Chatelier phenomenon, or dynamic strain aging, reveals itself as serrations upon plastic tensile deformation. This research evaluates this phenomenon when Al/NbB2 nanocomposite pellets are added to a magnesium-supersaturated Al matrix. A ball-milled 90 wt % Al and 10 wt % NbB2 nanocomposite helped inoculate an Al-Mg melt to incorporate the nanoparticles effectively. The melt was cast into rods that were cold-rolled into 1 mm diameter wires. Two sets were prepared: The first group was an as-cast set of samples, for comparison purposes, whereas the second was a solution-treated set. The solution treatment consisted of annealing followed by ice-water quenching. The results corroborating that the phenomenon was observable only in the specimens bearing the solution treatment, were used as the research baseline. Said treated alloy was compared to one containing the nanoparticles, which proved that the NbB2 particles caused a reduction of the serrated signal amplitude.

A numerical-experimental investigation of heat distribution, stress field and crack susceptibility in Ni60A coatings

3D finite element model (FEM) was built for the simulation of temperature and stress field induced by laser cladding. The proposed model was validated by experimental results. The numerical width and depth of coating matched well with the experimental cross-section of macrograph. The viscosity of molten pool versus the temperature field was also discussed, and the maximum difference of viscosity in different zones was approximately 32.8%. High temperature and sharp thermal gradient was generated in the vicinity of heat source, which was prone to produce residual stress. The heat distribution obtained from temperature field was in consistent with the thermocouple measurements. Due to large plastic tensile deformation of materials, the longitudinal residual stress was susceptible to crack propagation in the laser cladding. The measured maximum value of longitudinal residual stress reached 492 MPa, which was lower than predicts. The coatings were apt to crack along the vertical scanning direction. In addition, the crack susceptibility of coatings was not only depended on residual stress, but also the microsegregation of Cr, Ni and Fe elements. The calculation results are helpful for systematically understanding the melt pool, heat cycles, and stress, which related to laser cladding Ni-based materials.

Investigating the relationship between grain orientation and surface height changes in nickel polycrystals under tensile plastic deformation

This paper investigates the effect of the grain orientation on the surface roughening of nickel polycrystals undergoing plastic tensile deformation. Both experimental and simulation work was carried out. In the experiments, we measured the surface topography at different strain levels. The surface topography images were analyzed to classify individual grains as either rising or sinking. In simulations, we utilized a Crystal Plasticity Finite Element model that embeds a grain in an isotropic sample. This arrangement ensures that only the grain orientation of the embedded grain influences the grain surface topography. The average surface height of the grain was then calculated to classify its behavior to be rising or sinking. Both experiment and simulation results show that the grains with the loading direction close to the 〈001〉 and 〈111〉 lattice orientations tend to sink. For the rest of the grain orientations, the loading direction orientation, and thus the Schmid or Taylor factor, cannot uniquely determine whether the grain rises or sinks. A parametric study revealed that a grain's average surface height is contributed by the plastic deformation of the most stressed slip systems along the direction normal to the surface.

Computational and Experimental Fatigue Analysis of Contoured Spinal Rods

Posterior fixation with contoured rods is an established methodology for the treatment of spinal deformities. Both uniform industrial preforming and intraoperative contouring introduce tensile and compressive plastic deformations, respectively, at the concave and at the convex sides of the rod. The purpose of this study is to develop a validated numerical framework capable of predicting how the fatigue behavior of contoured spinal rods is affected by residual stresses when loaded in lordotic and kyphotic configurations. Established finite element models (FEM) describing static contouring were implemented as a preliminary simulation step and were followed by subsequent cyclical loading steps. The equivalent Sines stress distribution predicted in each configuration was compared to that in straight rods (SR) and related to the corresponding experimental number of cycles to failure. In the straight configuration, the maximum equivalent stress (441 MPa) exceeds the limit curve, as confirmed by experimental rod breakage after around 1.9 × 105 loading cycles. The stresses further increased in the lordotic configuration, where failure was reached within 2.4 × 104 cycles. The maximum equivalent stress was below the limit curve for the kyphotic configuration (640 MPa), for which a run-out of 106 cycles was reached. Microscopy inspection confirmed agreement between numerical predictions and experimental fatigue crack location. The contouring technique (uniform contouring (UC) or French bender (FB)) was not related to any statistically significant difference. Our study demonstrates the key role of residual stresses in altering the mean stress component, superposing to the tensile cyclic load, potentially explaining the higher failure rate of lordotic rods compared to kyphotic ones.

On the Origin of Peaks of Differential Magnetic Permeability in Low-Carbon Steels after Plastic Deformation

The physical origin of peaks in the field dependence of differential magnetic permeability of low-carbon steels after their plastic tensile deformation have been theoretically studied; they are caused by the irreversible displacements of the 90° domain walls. The angular difference between the [100] axes of the two neighboring grains with the large-angle boundaries has been determined; it corresponds to the peaks of differential permeability. It also controls the value of residual compressive stress. The results obtained are in perfect agreement with the corresponding experimental data.

Plastic anisotropy of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy

Tensile tests of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy specimens in different orientations were conducted, which indicates significant plastic anisotropy of this material. Digital image correlation method added in-situ-tensile tests were carried out to investigate mechanical properties with respect to specified material structures. The results indicate that the plasticity properties of the thick columnar grain and that of other grains are significant different. Under the same stress level, the thick columnar grain yield firstly and bear the main plastic deformation of the whole specimen. The elasto-plastic Poisson's ratio of the thick columnar grains and that of other grains are also different. Tests on layer bands indicate that the coarser microstructures of the layer bands lead a stronger resistance to tensile plastic deformation, but a weaker resistance to shear plastic deformation. In addition, the direction of primary α laths on both sides of the layer bands may be different, and this has an obviously effect on the tensile plastic deformation of the specimen.

A modified model of magneto-mechanical effect on magnetization in ferromagnetic materials

The prevailing Jiles-Atherton (J-A) model and Zheng Xiao-Jing-Liu Xing-En (Z-L) model are extensively used in modeling the magneto-mechanical effect on magnetization in ferromagnetic materials. In the J-A model, a fitting formula of magnetostrictive strain interms of stress and magnetization is adopted to model the stress effect on magnetostriction. However, the fitting formula is not in good accordance with the experimental results obtained by Kuruzar and Culllity. In order to solve this problem, a transcendental function tanh(<i>x</i>) is appropriately selected to describe the nonlinear magnetostrictive strain in the Z-L model, and it is found that the general formula of magnetostrictive strain is more effective to describe the nonlinear relation of magnetostrictive strain with stress and magnetization. Then, the modified law proposed by Jiles and Li is adopted to modify the Z-L model by Shi Pengpeng to describe the hysteretic behavior; nevertheless, the effect of Weiss molecular field, pinning energy and plastic deformation on magnetization are not taken into account, and the modified Z-L model can only describe the elastic stress effect on magnetization. In order to solve these problems above, a modified magneto-mechanical model is established by combining the magnetostrictive constitutive relationships of Z-L model with the modified energy conservation equation of J-A model, as well as taking the effect of elastic stress and plastic strain on the model parameters into account simultaneously. It is found that the predictions of proposed model here are in better accordance with the initial magnetization curves given by Jiles and Atherton and the hysteresis loops obtained by Makar and Tanner under different stresses and plastic deformation than those calculated by the J-A model and Z-L model. The correlation coefficients between experimental data and theoretical results calculated by the modified model are all over 0.98, which indicates that the modified model here is more effective than the existing model. A detailed study also performed to reveal the effects of the elastic tensile and compressive stress and plastic tensile and compressive strain on hysteresis loops, coercivity and remanence. The proposed model reveals that the area of hysteresis loop and coercivity increase nonlinearly with the stress and plastic deformation increasing, while the remanence decreases significantly; the effects of compressive stress and compressive plastic deformation on magnetization characteristic parameters above are more significant than those of tensile stress and tensile plastic deformation, which is consistent with the experimental trend. The proposed model can be used to quantitatively analyze the magneto-mechanical effect on the magnetization of ferromagnetism.